Crystal structure of 4-[(4-methylbenzyl)oxy]-N′-(4-nitrobenzylidene)benzohydrazide: a new hydrazone derivative

The title aroylhydrazone ether exists in an E-configuration with respect to the double bond of the hydrazone bridge and with an acyl–hydrazone (—CH=N—NH—CO—) torsion angle of 166.0 (3)°. The molecule exhibits a non-planar conformation, likely induced by packing requirements.


Chemical context
Hydrazones are a special class of Schiff bases, which can be obtained by condensation between an alkyl or aryl hydrazine and a carbonyl compound (aldehyde or ketone). The active pharmacophore group, -CH N-NH-C O-, present in a hydrazone is primarily responsible for its broad spectrum of biological aspects (Taha et al., 2013). The presence of tautomeric forms facilitates their coordination behavior in neutral or anionic species (Banna et al., 2022) with metal ions (Zü lfikarog lu et al., 2020). The chemical diversity and pharmacological accessibility of hydrazone and its derivatives paves the way for research exploring drug design and discovery (Verma et al., 2014).
In this context and in a continuation of our recent work (Banna et al., 2023), we report here on the synthesis and crystal-structure determination of another derivatized aroylhydrazone bearing an ether group.

Structural commentary
The molecular structure of the hydrazone compound is shown in Fig. 1. The acyl-hydrazone (-CH N-NH-C O-) group connects the p-nitrophenyl group and the central phenyl ring, which in turn is bound to the p-methylbenzyloxy fragment. An E-configuration is observed with respect to the double bond of the hydrazone bridge N2 C16. The N1-N2 bond length of 1.376 (4) Å is slightly shorter than that of 1.397 (4) Å determined in the corresponding derivative having a thienyl ring replacing the p-nitrophenyl group (Banna et al., 2023). On the other hand, the O2 C15 bond of 1.237 (4) Å is close to that determined in the thienyl derivative [1.236 (4) Å ], and typical of a ketonic linkage, while an equilibrium between the keto and enol forms is present in solution. The nitrophenyl group and the benzohydrazone fragment form a dihedral angle of 73.3 (1) while the terminal 4-methylbenzyl group is rotated by 80.9 (1) with respect to the central phenyl ring. Fig. 2 depicts a superimposition of the molecular structure of the title compound with the thienyl derivative (Banna et al., 2023). It is worth noting the different orientations of the carbohydrazide CO-NH-N moiety, likely induced by crystal-packing requirements.

Supramolecular features
The crystal packing is governed by hydrogen-bonding interactions (Table 1, with corresponding symmetry codes) realized between the imino group N1-H1 with carbonyl oxygen atom O2 ii of a symmetry-related molecule. This results in a monoperiodic arrangement parallel to the b axis. In addition, nonclassical C16-H16Á Á ÁO2 ii hydrogen bonds between a methine group and the carbonyl O atom and C21-H21Á Á ÁO4 iii between an aromatic C-H group and one of the nitro O atoms are also present, as shown in Fig. 3. The ribbons are further connected by C14-H14Á Á ÁN2 i interactions (Table 1). No significant -stacking interaction is found in the crystal (all centroid-to-centroid distances between phenyl rings are > 5.0 Å ).

Synthesis and crystallization
The synthesis of the compound follows a procedure previously described (Banna et al., 2023). To a solution of 4-[(4-methylbenzyl)oxy]benzoylhydrazine (0.25 g, 0.97 mmol in 20 ml of absolute ethanol), a solution of 4-nitrobenzaldehyde (0.14 g, 0.97 mmol) in 5 ml ethanol was added and the mixture was heated and refluxed for 2 h. A colorless precipitate was obtained, filtered off, and washed several times with hot ethanol to eliminate any types of starting materials prior to being dried in a desiccator. The title compound was recrystallized from a mixture of DMF and ethanol. Colorless crystals suitable for X-ray diffraction were obtained after 60 d of keeping the sample solution undisturbed.

Figure 3
Crystal packing of the title compound showing the mono-periodic arrangement parallel to the b axis built by N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds (dashed lines).

Figure 1
The molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Hydrogen atoms were placed at geometrical positions, except for the N-H hydrogen atom, the position of which was located in a difference-Fourier map and freely refined. The Flack parameter of À0.8 (9) indicates that the absolute structure cannot confidently be derived from the data based on Mo radiation.     (Brandenburg, 1999); software used to prepare material for publication: WinGX (Farrugia, 2012).

4-[(4-Methylbenzyl)oxy]-N′-(4-nitrobenzylidene)benzohydrazide
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.